1. Field of the Invention
The present invention relates to a temperature sensor in which a thermistor element is contained in a metal enclosure in a state where a pair of electrode wires for taking out signals are connected in an exposed manner at two opposing end surfaces thereof.
2. Description of the Related Art
There has heretofore been proposed a thermistor element in which a pair of electrode wires are connected to the two opposing end surfaces of the thermistor element in an exposed form to take out signals from the thermistor element, and the thermistor element is held by these electrode wires (hereinafter referred to as thermistor element of the type held by the electrode wires) as disclosed in Japanese Examined Patent Publication (Kokoku) No. 52-7535.
The thermistor element of the type held by the electrode wires is usually assembled by being inserted in a cylindrical metal enclosure, and is used as a temperature sensor. It has been desired to provide a temperature sensor which features further improved response characteristics for detecting the temperature (high-speed response characteristics).
In view of the above-mentioned problem, it is an object of the present invention to provide a temperature sensor obtained by containing, in a metal enclosure, a thermistor element of the type held by the electrode wires, which features improved response characteristics.
Concerning the response characteristics of the temperature sensor, the present inventors have regarded the time (response time) until a signal from the thermistor element represents 630xc2x0 C. as a reference for judgement under a condition where the temperature sensor is placed in an atmosphere of 1000xc2x0 C. and is heated up to 1000xc2x0 C. The response time, so far, is 6 seconds at the shortest.
The present inventors have considered that the response time can be decreased to shorter than 6 seconds if the distance between the metal enclosure and the thermistor element is decreased to be as small as possible, and have made a study concerning the distance between the metal enclosure and the thermistor element. The invention according to a first aspect is accomplished based on the results of this study.
Namely, according to the first aspect of the present invention, there is provided a temperature sensor comprising:
a metal enclosure 2;
a thermistor element 3 contained in the metal enclosure; and
a pair of electrode wires 4 connected to the two opposing end surfaces of the thermistor element in a form being exposed over the thermistor element in the metal enclosure to take out thermistor signals; wherein
a distance H between the thermistor element and the metal enclosure is not smaller than 0 but is not larger than 0.3 mm.
Namely, there is provided a temperature sensor having a response time shorter than 6 seconds, which was past the quickest response time, making it possible to achieve further increased response characteristics.
According to a second aspect of the invention, the metal enclosure 2 is of a cylindrical shape, the thermistor element is contained in the metal enclosure on the side of one end thereof, and a portion of the metal enclosure where the thermistor element 3 is contained, is a small-diameter portion 2a which is so draw-formed as to possess a diameter smaller than that of other portions of the metal enclosure.
By draw-forming the thermistor element-containing portion of the cylindrical metal enclosure, it is allowed to favorably realize the distance between the thermistor element and the metal enclosure as contemplated in the first aspect of the invention.
According to a third aspect of the invention, a sheath pin 6 is contained in the metal enclosure 2 on the other side thereof, the sheath pin 6 having core wires 6a electrically connected to the pair of electrode wires 4 and having a diameter larger than that of the thermistor element 3, wherein a portion of the metal enclosure between the portion 2c containing the sheath pin and the small-diameter portion 2a is so draw-formed as to possess a diameter larger than that of the small-diameter portion but is smaller than that of the portion containing the sheath pin.
This makes it possible to reduce the heat capacity by decreasing the size and volume of the metal enclosure in addition to obtaining the effect of the second aspect of the invention, and is desirable for improving the response characteristics.
To improve the response characteristics of the sensor, further, it is desired to decrease the diameter of the metal enclosure to reduce the heat capacity accompanied by a decrease in the size of the thermistor element. In this case, the thermistor element is realized in a size as contemplated in the fourth and fifth aspect of the invention as compared to the outer diameter of the sheath pin.
That is, according to the fourth aspect of the invention, a ratio D1/D2 of the outer diameter D1 of the sheath pin 6 to the diameter D2 of a circumscribed circle C of the thermistor element 3 is from 2 to 10 in the temperature sensor of the third aspect of the invention.
According to the fifth aspect of the invention, the outer diameter D1 of the sheath pin 6 is from 1.6 mm to 3.2 mm, and the diameter D2 of the circumscribed circle C of the thermistor element 3 is from 0.35 mm to 0.8 mm in the temperature sensor of the third aspect of the invention.
According to a sixth aspect of the invention, there is provided a temperature sensor comprising:
a metal enclosure 2 of a cylindrical shape;
a thermistor element 3 contained in the metal enclosure on the side of one end thereof;
a pair of electrode wires 4 connected to the two opposing end surfaces of the thermistor element in a form being exposed over the thermistor element in the metal enclosure, and extending to the side of the other end of the metal enclosure to take out thermistor signals; and
a sheath pin 6 contained in the metal enclosure on the other side thereof, the sheath pin 6 having core wires 6a electrically connected to the pair of electrode wires 4 and having a diameter larger than that of the thermistor element; wherein a portion of the metal enclosure, where the thermistor element is contained, is a small-diameter portion 2a; 
a distance H between the thermistor element in the small-diameter portion and the metal enclosure is not smaller than 0 but is not larger than 0.3 mm;
a portion of the metal enclosure where the sheath pin is contained, is a large-diameter portion 2c having a diameter larger than that of the small-diameter portion; and
a portion of the metal enclosure where the pair of electrode wires are contained, is an intermediate-diameter portion 2b having a diameter larger than that of the small-diameter portion but is smaller than that of the large-diameter portion.
According to this invention, the distance H between the thermistor element and the metal enclosure is not smaller than 0 but is not larger than 0.3 mm, making it possible to provide higher response characteristics as in the first aspect of the invention.
By draw-forming the cylindrical metal enclosure, further, the portion containing the thermistor element is formed to possess a small diameter, making it possible to favorably realize the distance between the thermistor element and the metal enclosure to be not smaller than 0 but not larger than 0.3 mm.
In draw-forming the portion of the metal enclosure where the thermistor element is contained, if this portion is draw-formed to possess a diameter as fine as the diameter of the electrode wire-containing portion between the sheath pin-containing portion and the thermistor element-containing portion, vibration of the metal cover easily transmits to the electrode wires often causing the electrode wires to be broken.
According to the present invention, therefore, the portion of the metal enclosure containing the electrode wires is draw-formed to be an intermediate-diameter portion to decrease the size and volume of the metal enclosure, so that the heat is favorably drawn and that the vibration of the metal enclosure is hardly transmitted to the electrode wires in the electrode wire-containing portion. It is, therefore, possible to improve the resistance of the electrode wires against the vibration.
According to the experiment and study conducted by the present inventors, when the outer diameter D1 of the sheath pin 6 is 1, it is desired that the inner diameter D3 of the intermediate-diameter portion 2b is not smaller than 0.5, the inner diameter D4 of the small-diameter portion 2a is not smaller than 0.25, the length L1 of the intermediate-diameter portion from the end of the sheath pin is not smaller than 3 mm, and the length L2 of the metal enclosure 2 extending from the end of the sheath pin to the side of the small-diameter portion is not larger than 16 mm as contemplated in a seventh aspect of the invention.
According to an eighth aspect of the present invention, an insulating member 5 is interposed among the thermistor element 3, the electrode wires 4 and the metal enclosure 2 to electrically insulate them from each other.
The metal enclosure may be brought into direct contact with the thermistor element. In this case, however, a leakage current may flow from the thermistor element into the metal enclosure to deteriorate the response characteristics. According to the present invention, on the other hand, the insulating member prevents the flow of leakage current, which is desirable from the standpoint of improving the response characteristics.
Here, according to a ninth aspect of the present invention, the thermistor element 3 and the metal enclosure 2 are in contact with each other via the insulating member 5, eliminating undesired gaps among the thermistor element, the insulating member and the metal enclosure, and making it possible to shorten the distance between the metal enclosure and the thermistor element as much as possible.
As the insulating member, there can be employed the electrically insulating layer 5 which is so formed as to cover the surfaces of the thermistor element 3 and of the electrode wires 4 (tenth aspect of the invention), or there can be employed the electrically insulating layer 5 formed on the inner surface of the metal enclosure 2 (eleventh aspect of the invention).
As the insulating member, further, there can be employed a crystallized glass or a ceramic as contemplated in a twelfth aspect of the invention.
Reference numerals attached to the above-mentioned means represent correspondence to concrete means described in the embodiments appearing below.